3 Months post liposuction: is swelling, bruising, and hardening normal in thighs?

Without seeing pictures, it is hard to say if what you are experiencing is normal or not.  Howeevr, for the amount of liposuction that you went through (4L), I would not be surprised if you are still healing and having contour changes.  That is a significant amount of removal, and can take quite awile for the tissues to recover from that.  I would listen to your plastic surgeon's advice and be patient.  I hope this helps.

This is a tough question to answer without actually seeing you. Yes, swelling and hardening can be normal for many months after liposuction. It can be caused by many things. Sometimes continuing the garment and massage of the hardened area can be helpful. The bruising is a less usual thing at this point after surgery. Sometimes this can be the sign of some bleeding (as can swelling and hardening). We call this a hematoma, but 3 months after liposuction it would very unusual to have spontaneous bleeding from the liposuction surgery.